The present invention relates to a system and method for dispersing a plurality of filaments. If these dispersed filaments are deposited on a moving web-forming surface, they will form a high machine-direction strength nonwoven product having a random, convoluted web pattern.
Filaments for use in the manufacture of nonwovens can be produced by various methods. For example, synthetic polymers can be spun into filaments. These spun filaments can be drawn-off by a high velocity jet system and directed onto a web-forming surface, as in the case of U.S. Pat. No. 3,692,618 to Dorschner. The use of these high velocity jets facilitates high draw-off speed so that relatively large numbers of filaments can be transported through the system on a continuous basis. A compressed fluid, such as air, is employed as the transporting means. However, some of these jet systems have a constriction at the exit of the flow path. The exit constriction creates a back-pressure on the jet system. This, in turn, requires exertion of a higher, primary pressure by the jets to overcome the resultant back-pressure and achieve the required filament velocity. This gives rise to wasted energy, and a higher cost of production ensues.
The above described prior art systems also have a narrow constriction at their inlet which causes the filaments to be moved through the system, and to exit therefrom, in close association with each other. Typically, a plurality of jet systems are spaced laterally across a moving web-forming surface. Therefore, in order to form a continuous web, in the cross-machine direction, this narrow stream of closely associated filaments must be laterally dispersed.
In an attempt to solve this lateral dispersion problem, some formation systems employ complex electrostatic charging apparatus (see U.S. Pat. No. 3,341,394 to Kinney).
Others try to achieve lateral dispersion of the filaments by directing continuous or intermittent air flows, essentially with a cross-machine direction, against vertically traveling filaments as they pass through an open area, after exiting from the high velocity jet system, in an effort to disperse same. In U.S. Pat. No. 3,485,428 to Jackson, for example, horizontally disposed, sequentially directed, in essentially a cross-machine direction, low-pressure fluid is intermittently supplied to a diverging chamber through which strands of yarn pass. The fluid which emanates from the two diametrically opposed jets impinges the high velocity system of filaments and exerts a pushing force or pressure on the filaments, in a reciprocating manner. This approach does not, however, cause heavy denier filaments or filaments moving at extremely high velocities, or substantial numbers of filaments, to be effectively dispersed in a manner required for nonwoven product formation. Instead, the entire filament aggregation is moved from side-to-side, as the filaments are impinged by the intermittently directed air flow, without causing effective dispersion thereof.
In another approach, the continuous or intermittent use of a phenomenon known as the "Coanda effect" can be imparted to filaments passing within an open area between opposed Coanda nozzles. The Coanda effect, which has been known for many years, is exemplified by U.S. Pat. No. 2,052,869 issued to Henri Coanda. Briefly, this phenomenon can be described as the tendency of a fluid, which emerges from an opening, such as a slit, under pressure, to attach itself or cling to and follow a surface in the form of an extended lip of the slit, which recedes from the flow access to the fluid as it emerges from the slit. This creates a zone of reduced pressure in the area of the slit so that any entrainable material which is in the area will be entrained and flow with the fluid which has attached itself to the extended lip.
On commonly owned, pending application U.S. Ser. No. 68,246, for example, an oscillating movement essentially in a cross-machine direction is imparted to the filaments by a pulsating fluid which causes non-steady-state conditions between opposed Coanda nozzles. The use of Coanda nozzles to oscillate filaments exiting a high velocity jet stream, however, requires individual separators for supplying filaments to the open area between the opposed Coanda nozzles. However, the above described separators can exhibit plugging problems, create back-pressure in the jet air guns, and limit filaments' through-put rates. Moreover, they deliver the filaments to the web-forming means in a substantially parallel lay-down pattern so that the web formed is essentially a structure of more or less parallel filaments. The machine-direction strength of webs formed by this technique is insufficient for many converting operations, for example, in diaper liners, and the like.